This game was developed with Flash/ActionScript and later ported to HTML5/Dart. The outer tunnel is rendered with a Shape where the Graphics instance is cleared and updated at every frame. The obstacles are BitmapDatas zoomed with Bitmaps. The collision check is achieved by checking the alpha-channel of the BitmapData at the point of fly through. A mask limits the outer bounds of the tunnel.
Special thanks to www.funwin.com for providing the Flash source code and artwork of this game.